1. Field of the Invention
The present invention relates to the treatment of contaminated materials. Specifically, it relates to methods and compositions for rendering inert a broad spectrum of heavy metals that may be present in hazardous and/or toxic matrices such as fly ash and slag from incinerators; process water from ink and paint manufacturing; process dust, water and sludge from ferrous and non-ferrous foundries; electric arc furnace dust, for example, from steel mills; hazardous waste, toxic waste, soils, sludges and sediments. Heavy metals including antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, lead, mercury, molybdenum, nickel, selenium, silver, thallium, vanadium and zinc are reduced to a level of permanent stability meeting the glacial acetic acid leachate criteria set forth by the U.S. EPA in the Toxicity Characteristic Leaching Procedure (TCLP) and the water leach tests, for example, California or Indiana Water Leach Test, simulating leaching due to rain as it actually occurs in the environment, the most recent versions of such procedure and tests as of Feb. 1, 1998, incorporated herein by reference. The invention also relates to industrial processes that require acid gas removal from a contaminated matrix and pH control of a contaminated matrix.
2. Discussion of the Background
When biologically available, heavy metals leaching from soil, water or waste, as well as those released into the air are detrimental to all living beings. Permissible levels of heavy metal pollution are regulated by the local, state and federal authorities. Important sets of federal regulations include the Resource Conservation and Recovery Act (RCRA) and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), which governs the Superfund program. One of the earliest remediation methods, the removal and hauling of heavy metal contaminated waste and soil to a landfill, while still in use, is being viewed by the public and the press as unacceptable. New regulations and continued desire to find better and/or inexpensive environmental pollution control, prevention and remediation techniques have driven potential hazardous and/or toxic waste generators toward new technologies. Encapsulation of heavy metal contaminated waste in Portland cement, for example, though meeting the letter of the environmental law, does not meet the spirit of the law when the encapsulated waste is exposed to rain. Heavy metals go into solution and become biologically available. Permanent stabilization by forming geochemically stable compounds of heavy metals is by far the best solution to this challenge. Certain industrial processes may also release acid gases which need to be removed. Often pH control of the contaminated matrix is also required.
Numerous methods, mostly multi-step and sequential-step, have been utilized to prevent the leaching of hazardous heavy metals in solid, semi-solid, liquid and/or gaseous complex matrices so that the waste is rendered suitable for disposal in a sanitary landfill. There has, however, been no suggestion to use sulfur-containing material such as magnesium sulfite (scrubber magnesium product) and/or boron-containing material such as hydroboracite for the purpose of providing heavy metal stabilization; to use hydroboracite, by itself for acid gas removal and pH control of the contaminated or treated matrix. Furthermore, there has been no suggestion of the use of phosphates such as triple super phosphate, phosphate rock, fines generated from screening and combining of phosphate fertilizers (TSP (triple super phosphate), MAP (monoammonium phosphate), DAP (diammonium phosphate), etc.) along with magnesium sulfite (scrubber magnesium product) and/or hydroboracite and/or limestone for the purpose of providing heavy metal stabilization, together with the additional benefits of acid gas removal and pH control, to contaminated or treated matrices in a single-step method or single-product composition.
U.S. Pat. No. 4,671,882 to Douglas discloses a multi-step process for heavy metal stabilization. Douglas does not prefer to use limestone because he believes that the use of limestone results in the production of carbon dioxide gas when added to acid solution and such gas would adversely affect the pH increasing step essential to his multi-step heavy metal stabilization process. Both U.S. Pat. Nos. 4,889,640 and 5,037,479 to Stanforth teach away from the use of limestone in his single-step and sequential-step heavy metal stabilization processes because he considers it as a non-reactive form of calcium and/or magnesium carbonate and a hinderance to heavy metal stabilization. The above-mentioned patents do not suggest any products or processes for acid gas removal.